An led drive circuit connectable to a phase control type light adjuster includes a first reference voltage generation portion that generates a first reference voltage, a second reference voltage generation portion that generates a second reference voltage according to a phase angle of the light adjuster, an input voltage detection portion that detects a size relationship between an input voltage and a threshold value voltage, a current draw-out portion that draws out a current in accordance with the first reference voltage or the second reference voltage from an electricity supply line that supplies electricity to an led drive portion, and a switch portion that in accordance with a detection result by the input voltage, detection portion, performs switching between an output from the first reference voltage generation portion to the current draw-out portion and an output from the second reference voltage generation portion to the current draw-out portion.
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1. An led drive circuit which is connectable to a phase control type light adjuster and into which an input voltage based on an a.c. voltage that undergoes phase control performed by the phase control type light adjuster is input to drive an led load, comprising:
an led drive portion that drives the led load;
a phase angle detection portion that detects a phase angle based on the input voltage;
a first reference voltage generation portion that generates a first reference voltage;
a second reference voltage generation portion that generates a second reference voltage in accordance with the phase angle detected by the phase angle detection portion;
an input voltage detection portion that detects a size relationship between the input voltage and a threshold value voltage;
a current draw-out portion that draws out a current in accordance with the first reference voltage or the second reference voltage from an electricity supply line that supplies electricity to the led drive portion; and
a switch portion that in accordance with a detection result by the input voltage detection portion, performs switching between an output from the first reference voltage generation portion to the current draw-out portion and an output from the second reference voltage generation portion to the current draw-out portion.
10. An led illumination apparatus comprising:
an led drive circuit which is connectable to a phase control type light adjuster and into which an input voltage based on an a.c. voltage that undergoes phase control performed by the phase control type light adjuster is input to drive an led load, including:
an led drive portion that drives the led load,
a phase angle detection portion that detects a phase angle based on the input voltage,
a first reference voltage generation portion that generates a first reference voltage,
a second reference voltage generation portion that generates a second reference voltage in accordance with the phase angle detected by the phase angle detection portion,
an input voltage detection portion that detects a size relationship between the input voltage and a threshold value voltage,
a current draw-out portion that draws out a current in accordance with the first reference voltage or the second reference voltage from an electricity supply line that supplies electricity to the led drive portion, and
a switch portion that in accordance with a detection result by the input voltage detection portion, performs switching between an output from the first reference voltage generation portion to the current draw-out portion and an output from the second reference voltage generation portion to the current draw-out portion; and
an led load that is connected to an output side of the led drive circuit.
2. The led drive circuit according to
the first reference voltage generation portion generates the first reference voltage in accordance with the phase angle detected by the phase angle detection portion.
3. The led drive circuit according to
in a case where the phase angle detected by the phase angle detection portion is near 0°, the first reference voltage generation portion generates the first reference voltage at which the current draw-out portion does not draw out a current.
4. The led drive circuit according to
when the input voltage detection portion detects that the input voltage is equal to or smaller than the threshold value voltage, the led drive portion stops switching.
5. The led drive circuit according to
when the phase angle detected by the phase angle detection portion is in a range of 0° to 90°, the second reference voltage generation portion generates the second reference voltage at which the current draw-out portion does not draw out a current, and generates the second reference voltage at which as the phase angle detected by the phase angle detection portion becomes larger than 90°, the current drawn out by the current draw-out portion increases.
6. The led drive circuit according to
when the phase angle detected by the phase angle detection portion is equal to or larger than a predetermine phase angle that is larger than 90°, the second reference voltage generation portion generates the second reference voltage at which the current drawn out by the current draw-out portion becomes constant.
7. The led drive circuit according to
when the phase angle detected by the phase angle detection portion becomes larger than a predetermined phase angle, the led drive portion turns off the led load; and
as the phase angle detected by the phase angle detection portion becomes larger than the predetermined phase angle, the second reference voltage generation portion generates the second reference voltage at which the current drawn out by the current draw-out portion decreases to zero.
8. The led drive circuit according to
the second reference voltage generation portion varies the second reference voltage that is generated during a half period of an a.c. period.
9. The led drive circuit according to
the phase angle detection portion detects the phase angle at every half period of an a.c. period.
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This application is based on Japanese Patent Application No. 2011-210485 filed on Sep. 27, 2011, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an LED drive circuit and an LED illumination apparatus that uses the same.
2. Description of the Related Art
An LED (Light Emitting Diode) has features of low current consumption and long life and the like, and is finding its wide applications in not only a display apparatus but also an illumination apparatus and the like. Here, in an LED illumination apparatus, there are many cases where a plurality of LEDs are used to obtain a desired illuminance (e.g., see JP-A-2004-327152, JP-A-2005-11739, and JP-A-2011-28954).
A general illumination apparatus often uses a commercial a.c. power supply, and considering a case where an LED illumination apparatus is used instead of a general illumination apparatus such as an incandescent lamp and the like, it is desirable that like the general illumination apparatus, the LED illumination apparatus also is structured to use a commercial a.c. power supply.
Besides, in a case of performing light adjustment control of an incandescent lamp, a phase control type light adjuster (generally, called an incandescent lamp controller) is used, which is capable of easily performing light adjustment control of electricity supply to the incandescent lamp by means of a volume device only by turning on a switching device (generally, a thyristor and a TRIAC device) at a phase angle of an a.c. power supply voltage. However, in the case of performing light adjustment of an incandescent lamp by means of a phase control type light adjuster, it is known that when the light adjuster is connected to the incandescent lamp that has a small wattage, flickering and blinking occur and normal light adjustment is impossible.
In a case of performing light adjustment control of an LED illumination apparatus that uses an a.c. power supply, it is desirable that an existing phase control type light adjuster for an incandescent lamp is connectable as it is. By using an existing facility for light adjustment and an LED illumination apparatus as the illumination apparatus, it becomes possible to achieve dramatic power consumption reduction compared with the incandescent lamp. Besides, it is possible to secure compatibility without changing the facility for light adjustment to a facility dedicated to the LED illumination apparatus, which leads to reduction in facility cost.
Here,
In the case where the LED array composed of the LEDs connected in series is connected to the phase control type light adjuster for an incandescent lamp; the phase angle of the phase control type light adjuster is made larger; and the brightness of the LEDs is made lower, when an output voltage from the diode bridge becomes smaller than a forward voltage at which the LED array begins to shine, the LEDs come not to shine and the current flowing to the light adjuster rapidly decreases. When the current flowing to the light adjuster rapidly decreases, the current flowing to the TRIAC in the light adjuster becomes lower than a hold current, accordingly, the TRIAC is turned off and output from the light adjuster stops and becomes unstable, whereby flickering occurs in the brightness of the LEDs. Besides, when the light adjuster output undergoes phase control and the TRIAC changes from an off-state to an on-state, the LEDs change from an off-state to an on-state, whereby impedance of the LEDs rapidly changes. According to this, there is a case where ringing occurs in an edge portion where an output voltage from the light adjuster rapidly changes; the TRIAC becomes unstable and is turned off; and flickering occurs in the brightness. A phenomenon occurs in which the timing the TRIAC is turned off deviates at every half period of the alternating current; and the TRIAC is unstable between turning-off and turning-on, whereby flickering occurs. Besides, there is also a case where the TRIAC, which is once turned off, is turned on after a time span; an oscillation phenomenon occurs in which the on/off repeats; and flickering occurs.
Besides, there are many cases where to achieve power factor improvement and EMI noise reduction, a filter circuit, which includes a resistor; an inductor; a diode; and a capacitor, is disposed between the diode bridge and the LED drive circuit. When the phase angle of the light adjuster becomes equal to or larger than 90°, the current flowing to the LED drive circuit decreases thanks to light adjustment operation of the LED drive circuit, and the output voltage from the light adjuster changes from increasing to decreasing, accordingly, the LED drive circuit operates thanks to electric charges accumulated in the capacitor in the filter circuit. According to this, there is a case where the current supplied from the light adjuster decreases rapidly; the current in the TRIAC in the light adjuster becomes lower than the hold current; the TRIAC is turned off and the light adjuster malfunctions; and flickering occurs.
Here, in the case of the conventional incandescent lamp load, the load is a filament formed of tungsten or the like, accordingly, at the time the TRIAC of the light adjuster is switched from the off-state to the on-state, the impedance change is less and the impedance keeps a low impedance state. Besides, there are not the diode bridge and the filter circuit, accordingly, the current flowing to the light adjuster does not change rapidly, and the stable light adjustment operation is possible until the a.c. power supply reaches near 0 V.
It is an object of the present invention to provide an LED drive circuit and an LED illumination apparatus that are capable of alleviating flickering of an LED and achieving efficiency improvement.
The present invention is an LED drive circuit which is connectable to a phase control type light adjuster and into which an input voltage based on an a.c. voltage that undergoes phase control performed by the phase control type light adjuster is input to drive an LED load, including:
an LED drive portion that drives the LED load;
a phase angle detection portion that detects a phase angle based on the input voltage;
a first reference voltage generation portion that generates a first reference voltage;
a second reference voltage generation portion that generates a second reference voltage in accordance with the phase angle detected by the phase angle detection portion;
an input voltage detection portion that detects a size relationship between the input voltage and a threshold value voltage;
a current draw-out portion that draws out a current in accordance with the first reference voltage or the second reference voltage from an electricity supply line that supplies electricity to the LED drive portion; and
a switch portion that in accordance with a detection result by the input voltage detection portion, performs switching between an output from the first reference voltage generation portion to the current draw-out portion and an output from the second reference voltage generation portion to the current draw-out portion.
According to this structure, the current drawing-out based on the first reference voltage and the current drawing-out based on the second reference voltage are performed independent of each other and the current drawn out in accordance with the phase angle is varied, accordingly, it is possible to curb flickering of the LED by alleviating a current control means (e.g., a TRIAC and the like) in the phase control type light adjuster being turned off and to achieve efficiency improvement.
Besides, the first reference voltage generation portion may generate the first reference voltage in accordance with the phase angle detected by the phase angle detection portion.
Besides, in a case where the phase angle detected by the phase angle detection portion is near 0°, the first reference voltage generation portion may generate the first reference voltage at which the current draw-out portion does not draw out a current.
Besides, when the input voltage detection portion detects that the input voltage is equal to or smaller than the threshold value voltage, the LED drive portion may stop switching.
Besides, when the phase angle detected by the phase angle detection portion is in a range of 0° to 90°, the second reference voltage generation portion may generate the second reference voltage at which the current draw-out portion does not draw out a current, and may generate the second reference voltage at which as the phase angle detected by the phase angle detection portion becomes larger than 90°, the current drawn out by the current draw-out portion increases.
Besides, when the phase angle detected by the phase angle detection portion is equal to or larger than a predetermine phase angle that is larger than 90°, the second reference voltage generation portion may generate the second reference voltage at which the current drawn out by the current draw-out portion becomes constant.
Besides, when the phase angle detected by the phase angle detection portion becomes larger than a predetermined phase angle, the LED drive portion may turn off the LED load; and
as the phase angle detected by the phase angle detection portion becomes larger than the predetermined phase angle, the second reference voltage generation portion may generate the second reference voltage at which the current drawn out by the current draw-out portion decreases to zero.
Besides, the second reference voltage generation portion may vary the second reference voltage that is generated during a half period of an a.c. period.
Besides, the phase angle detection portion may detect the phase angle at every half period of the a.c. period.
Besides, an LED illumination apparatus according to the present invention is structured to include the LED drive circuit having any one of the above structures and an LED load that is connected to an output side of the LED drive circuit.
Hereinafter, an embodiment of the present invention is described with reference to drawings.
The LED illumination system shown in
The commercial power supply 100 outputs a sine-wave a.c. voltage; the voltage differs depending on countries: there are voltages of 100 V to 250 V and frequencies of 50 Hz and 60 Hz. When the a.c. voltage is input into the phase control type light adjuster 200, in accordance with rotation or slide operation of a volume for performing light adjustment, a waveform cut out at a phase point of the a.c. waveform is generated. The output waveform from the phase control type light adjuster 200 undergoes full-wave rectification performed by the diode bridge DB1, and a pulsation waveform, which has a frequency two times (100 Hz in a case of 50 Hz, 120 Hz in a case of 60 Hz) as high as the input frequency, is input to an input terminal T0 of the LED drive circuit 500.
The LED drive circuit 500 has: a filter circuit 1; an input voltage detection portion 2; a phase angle detection portion 3; a first reference voltage generation portion 4; a second reference voltage generation portion 5; a current draw-out portion 6; and an LED drive portion 7.
The filter circuit 1, which aims to achieve power factor improvement and reduce EMI noise radiated to outside by attenuating switching noise of the LED drive portion 7, is, as shown in
Based on an input voltage VIN that is input from the diode bridge DB1 to the input terminal T0, the phase angle detection portion 3 detects a phase angle of the phase control type light adjuster 200. The LED drive portion 7 varies a current to be flown to the LED array 400 in accordance with the phase angle detected by the phase angle detection portion 3, thereby performing the light adjustment.
The first reference voltage generation portion 4 and the second reference voltage generation portion 5 generate a reference voltage that corresponds to the phase angle detected by the phase angle detection portion 3. The input voltage detection portion 2 detects whether the input voltage VIN is equal to or smaller than a predetermined threshold value voltage, and switches a switch SW1 in accordance with the detection result.
Upon detecting that the input voltage VIN is equal to or smaller than the threshold value voltage, the input voltage detection portion 2 switches the switch SW1 such that the first reference voltage output from the first reference voltage generation portion 4 is input into the current draw-out portion 6. On the other hand, upon detecting that the input voltage VIN exceeds the threshold value voltage, the input voltage detection portion 2 switches the switch SW1 such that the second reference voltage output from the second reference voltage generation portion 5 is input into the current draw-out portion 6. The current draw-out portion 6 draws out a current, which is proportional to the first reference voltage or the second reference voltage, from a electricity supply line LN1 that supplies electricity to the LED drive portion 7.
Because of this reason, as shown in
Besides,
In a case where
When the input voltage VIN exceeds the threshold value voltage, the second reference voltage in accordance with the detected phase angle is input into the current draw-out portion 6, and a current proportional to the second reference voltage is drawn out by the current draw-out portion 6, accordingly, it is possible to prevent the TRIAC Tri in the light adjuster 200 from being turned off and to improve the efficiency by drawing out a suitable amount of current. Besides, when the input voltage VIN is equal to or smaller than the threshold value voltage, the first reference voltage is input into the current draw-out portion 6, and a current proportional to the first reference voltage is drawn out by the current draw-out portion 6, accordingly, it is possible to prevent the TRIAC Tri from being turned off when the LED array 400 is turned off. Besides, the reference voltage is switched for an on-time span and an off-time span of the input voltage VIN to vary the drawn-out current, accordingly, it is possible to improve the efficiency. As described above, by preventing the TRIAC from being turned off, it is possible to achieve the light adjustment that alleviates flickering and hysteresis of the brightness (conventionally, when the phase angle of the light adjuster is changed from small→large and large→small, hysteresis occurs in the brightness of the LED).
Here, the first reference voltage may be set at a constant value irrespective of the phase angle of the light adjuster 200. In other words, the first reference voltage may not be invariably generated in accordance with the detected phase angle.
Besides, during a low voltage time span when the first reference voltage is selected (in other words, when the input voltage detection portion 2 detects that the input voltage VIN is equal to or smaller than the threshold value voltage), the switching of the LED drive portion 7 may be stopped. In the case where the LED drive portion 7 is composed of a flyback converter (e.g.,
Ton=L1×Ion/Vin
Besides,
Besides,
Because of this, in the present embodiment, as shown in
In the above structure, when the divided voltage by the resistors R33, R34 is equal to or smaller than the reference voltage VL, the input voltage input from the input terminal T3 is regarded as 0 V, the switches SWL, SWH are turned on, the voltage VPHASE becomes the reference voltage VB, and the capacitor C32 is charged. And, when the divided voltage by the resistors R33, R34 exceeds the reference voltage VL but is equal to or smaller than the reference voltage VH, it is deemed that the input voltage does not rise yet, the switch SWL is turned off and the switch SWH is in an on-state, accordingly, the capacitor C32 is discharged by the constant current source I1. And, when the divided voltage by the resistors R33, R34 exceeds the reference voltage VH, it is deemed that the input voltage rises, the switches SWL, SWH are turned off, and the discharge of the capacitor C32 is stopped. According to this operation, it is possible to generate the voltage VPHASE in accordance with a time span during which the input voltage rises from 0 V, that is, the phase angle.
Hereinbefore, the embodiments of the present invention are described; however, the embodiments are variously modifiable within the scope of the spirit of the present invention.
Shimizu, Takayuki, Murata, Takeshi, Kanamori, Atsushi, Warita, Hirohisa
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| Sep 10 2012 | WARITA, HIROHISA | Sharp Kabushiki Kaisha | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 028972 | /0148 | |
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